Boot tightener



FIG. 1 is a left, front perspective view of a boot tightener, showing my new design;

FIG. 2 is a right front perspective view thereof;

FIG. 3 is a left front perspective view thereof, in a closed condition; and,

FIG. 4 is a front perspective view of FIG. 3, the boot shown in broken lines for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a boot tightener, as shown and described. 